1. Field of the Invention
The invention relates to a protection circuit, and more particularly to a protection circuit for word lines in a memory array.
2. Description of the Prior Art
A well known cause of failure for electronic integrated circuits is plasma damage on gate devices. For example, during the wiring process, connections can be made which are electrically floating until they are connected again by the last wiring layer. In the meantime, however, electric charge caused, for example, by plasma etching, may accumulate on these floating connections. If one of these connections is coupled to the polygate of a transistor, the charges may leak to the gates via the connections, whereby it may exceed a maximum value and, thus, cause irreparable damage to the gates.
For simple integrated circuits, the charge may be discharged by a parasitic diode through a decoder circuit coupled to a memory array. However, when the integrated circuits are becoming complicated, it is difficult to discharge in time positive or negative charges by exterior decoder circuit.
It is an object of the present invention to provide a protection circuit for a memory array. Back-to-back diodes are used as a protection circuit can in time discharge positive or negative charges during plasma process.
It is another object of the present invention to provide a protection circuit coupled to multitude of word lines in a memory array. The parallel diodes coupled to the word lines and an in-common diode are arranged in series can save area consumption of the integrated circuits.
It is further object of the present invention to provide a protection structure for a memory array. The protection structure enables the memory array operated under positive or negative voltage.
In the present invention provides a protection circuit comprising one diode wherein the diode is formed by diffusing a heavily doped material of a first conductivity type into a first region of a second conductivity type. An integrated circuit, such as a memory array, is coupled to the diode. The other diode back-to-back is coupled to the diode wherein the other diode is formed by diffusing a heavily doped material of the second conductivity type into the first region and a second region of the first conductivity type. The two diodes in series are capable of discharging for the memory array during manufacturing process.